1. Field of the Invention
The present invention relates to a diaphragm valve; and more particularly relates to a weir-type diaphragm valve.
2. Brief Description of Related Art
FIGS. 1a and 1b show a diaphragm valve that is known in the art. In such a diaphragm valve, the diaphragm requires two mechanisms to make the valve work in both pressure and vacuum service conditions. A closing force, provided through the compressor (1), and an opening force, applied through the diaphragm stud (2), can be applied in numerous ways. Normally, a diaphragm stud is located in the center of the diaphragm. The stud and stud retention components create a non-uniformity in the sealing gasket cross section. This non-uniformity interrupts the pressure applied to the contact surface between the weir and diaphragm along the sealing bead of the valve body. This interruption can cause inconsistency of sealing for three reasons:                1) If the stud is too long or adjusted improperly, it can result in over compression of the diaphragm in the center, causing poor valve sealing characteristics and possible damage to the diaphragm.        2) If the stud is too short or adjusted improperly, it can result in under compression of the diaphragm in the center, causing poor valve sealing characteristics.        3) The transition area between the center seal line under the stud and the side seal line of the compressor may not experience the required seal pressure even if the pressure under the aforementioned components are balanced.        
It is noted that the peripheral seal of the valve body is independent of the aforementioned weir portion sealing and is made by components omitted from FIGS. 1a, 1b. 